Which of these sentences is correct? As it happens, the first is an actual quote (H. C. Wood, 1879)1(p445) and so in that sense is the “correct” one. However, the question remains: What are the differences, if any, between disease and disorder? For that matter, where does the often-used condition fit in? While these terms are frequently used interchangeably, differences between them do exist and can assist the person wishing to use them in more specific senses.

Condition is perhaps the least specific, often denoting states of health considered normal or healthy but nevertheless posing implications for the provision of health care (eg, pregnancy). The term might also be used to indicate grades of health (eg, a patient might be described as in stable, serious, or critical condition). While this term is often used in medical discussions to specifically indicate the presence of pathology or illness, Dorland’s Illustrated Medical Dictionary provides no definition of the term used in this sense. Merriam-Webster’s Collegiate Dictionary, however, defines condition as “a usu. defective state of health,”2(p258) and the Oxford English Dictionary similarly opines that it denotes “[a] state of health, esp. one which is poor or abnormal; a malady or sickness.”1(p309) In lay conversation condition is sometimes used euphemistically when a discreet term is desired for reference to a state of health, either well or ill—for example, delicate condition was once commonly used to refer to either pregnancy or alcoholism. Similarly, condition understood specifically to indicate the presence of pathology or illness is sometimes used as a value-neutral term when a stronger term might not be desirable. When such considerations do not come into play, a condition conferring illness can be further classified as a disease or a disorder.

“He was full of such disease. That he may nought the deth escape” (1393).1(p445)

Disease is often used in a general sense when referring to conditions affecting a physical system (eg, cardiovascular disease) or a part of the body (eg, diseases of the foot). The term also may be used in specific senses—for example, a writer might refer in general terms to neurologic disease or in specific terms to Alzheimer disease. But disease is perhaps most often used when referring to a condition that possesses specific characteristics. In this vein, Merriam-Webster’s defines disease as “a condition of the… body or one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms…”2(p358); the Oxford English Dictionary defines the word similarly but particularly stresses structural change as a cause.1(p445)Dorland’s concurs with these sources but makes clear that the impaired functioning associated with the diseased state may constitute “any deviation from or interruption of the normal structure or function…” and further elaborates that “the etiology, pathology, or prognosis may be unclear or unknown.”3(p535)

“A Fever is the first disorder that affects the Blood and Vessels” (1725).1(p449)

Compared with disease, disorder is less restrictive: Merriam-Webster’s defines it simply as “an abnormal physical or mental condition,”2(p360) a definition with which Dorland’s largely concurs.3(p555) The Oxford English Dictionary emphasizes that disorder involves a disturbance of function but again further stresses structural change, this time in negative terms, stating that disorder is “usually a weaker term than DISEASE, and not implying structural change.”1(p449) This emphasis on functional rather than structural change has been in place since at least the late 1800s, when the Lexicon of Medicine and Allied Sciences stated that disorder is “a term frequently used in medicine to imply functional disturbance, in opposition to manifest structural change.”1(p449) Because disorder, like condition, is relatively value-neutral when compared with disease, it is often used in place of the latter term when a less stigmatizing or less alarming term is desirable—eg, a clinician might at first refer to a patient’s disease as a disorder to reduce the patient’s initial anxiety; similarly, the same patient might initially refer to his or her recently diagnosed disease as a disorder in conversations with family and friends.

In short, what distinguishes condition, disease, and disorder from one another would seem to be their relative emphases on functional change, structural change, presence of signs and symptoms, and, perhaps to a lesser extent, the gravity a writer wishes to convey:

• Condition simply indicates a state of health, whether well or ill; a condition conferring illness might be further classified as a disease or a disorder—however, condition might be used in place of disease or disorder when a value-neutral term is desired.
• Disease denotes a condition characterized by functional impairment, structural change, and the presence of specific signs and symptoms. As an aside, Dorland’s equates the terms illness and sickness with disease; while these are often used to indicate the state or experience of disease, they are also sometimes used as value-neutral alternatives for disease.
• Disorder, in contrast, denotes a condition characterized by functional impairment without structural change and, while certain disorders or categories of disorders might be accompanied by specific signs and symptoms, their presence is not required for a condition to be termed a disorder. Like condition, disorder is sometimes used as a value-neutral term in place of disease.—Phil Sefton, ELS

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Thank you very much for this. I was inspired to search for this information as part of building a database of required competencies for my internal medicine program. As our genetic and molecular biology knowledge expands, it seems to me that number of disorders (functional impairment without structural change) will shrink or disappear entirely.